Thyristor valve is the key element of the high voltage direct current transmission. Its development and application has many years history. The traditional HVDC thyristor valve module is centered as the series connection thyristor valves structure; furthermore it also has the control system, trigging system and the protection system. Considering the safety of the thyristor valve, the module also includes the following auxiliary elements: saturated reactor, thyristor valve unit, damped resistor unit, damped capacitor unit, direct current equalizing resistance, acquiring energy resistance, control unit of thyristor valves, trigging unit of thyristor valves, protection unit of thyristor valves and water cooling system to meet the requirement. According to the rank of thyristor valves and the requirement to transmission power, choose suitable category. These elements, control units and water cooling system are effectively integrated together to form a thyristor valve module.
At present, the operation thyristor valves have some problems and disadvantages, such as easy leakage, high weight, and large structural size, difficult to install and repair. Leakage is the most key factor to affect the thyristor valves operation safely. And the weight and the structure are related with the manufacture cost, the convenience of the installation and the repair. The installation and repair are related with the operability and work efficiency of the engineering application.
Now there are mainly two forms about the thyristor valves structure design, frame structure and module distributed structure design. For frame structure design, there are two compositions, metallic frame structure and metallic composition and large size insulated beam mixture frame structure. Frame is the support of the valves module; there are various elements in the frame. For the metallic frame structure, the support strength is great, but the insulation problem of the air with metal is worth considering on high voltage condition. This will increase the size and the weight of the module frame, and waste the inner module space. For the mixture frame structure, there are mechanical strength problems. Because the module frame needs to take great weight load, it needs higher the structural strength of the insulated channel/beam, such as higher tensile strength, higher bending strength and higher shearing strength. This will increase module design difficulty and manufacture cost, and hamper the engineering application. For module distributed structure design, the inner elements of the module, such as thyristor valves, damped resistors, damped capacitors, gate series units, saturated reactors and so on, are all modular assembled. There are too much distributed valve modules in this structure design. This will increase the project site assembled difficulty; it is also harmful to improve the installation efficiency. What's worse, this distributed modules design increase the project site installation precision. It is very difficult for the operators to install the modules. It needs much higher level operator to accomplish the installation.
Now the working thyristor elements upgrade very slowly, and most of them are not the up-date technology products. They have not been met the requirement of the direct current transmission and high capacity.